Trans-impedance amplifier, chip, and communications device

ABSTRACT

A trans-impedance amplifier (TIA) includes a first circuit, a second circuit, and a third circuit. Both the first circuit and the second circuit are coupled to a current source, an operational amplifier, and the third circuit. The first circuit is configured to receive a first current, provide a third voltage to the third circuit, perform shape filtering on the first current, and convert the shape filtered first current to a first voltage for output. The second circuit is configured to receive a second current, provide a fourth voltage to the third circuit, perform shape filtering on the second current, and convert the shape filtered second current to a second voltage for output. The third circuit is configured to cooperate with the first circuit and the second circuit in performing shape filtering. The operational amplifier is configured to provide a small-signal virtual ground point to the first circuit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No.201710099963.5 filed on Feb. 23, 2017, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

This application relates to the field of chip technologies, and inparticular, to a trans-impedance amplifier (TIA), a chip, and acommunications device.

BACKGROUND

A TIA may be configured to convert a current signal to a voltage signal,and is widely applied to a receiving part of a sensor and a radiofrequency transceiver system.

Currently, commonly used TIAs are a TIA of a first-order activestructure shown in FIG. 1A and a TIA of a second-order active structureshown in FIG. 1B. Further, the TIA of the first-order active structureshown in FIG. 1A includes only one operational amplifier, and has anadvantage in terms of power consumption compared with the TIA of thesecond-order active structure shown in FIG. 1B, but the TIA of thefirst-order active structure has lower filtering capability. The TIA ofthe second-order active structure shown in FIG. 1B can performsecond-order shaping filtering on an input current, and therefore has arelatively strong out-of-band interference suppression capability.

In conclusion, TIAs of common structures at present all have performancebottlenecks.

SUMMARY

This application provides a TIA, a chip, and a communications device, toresolve a problem that power consumption of a TIA cannot be reduced whenfiltering performance thereof is improved.

According to a first aspect, a TIA is provided, including a firstcircuit, a second circuit, a third circuit, and an operationalamplifier, where each of the first circuit, the second circuit, and thethird circuit includes a passive component. The first circuit isconnected to a current source, the operational amplifier, and the thirdcircuit, and is configured to receive a first current provided by thecurrent source, provide a third voltage to the third circuit based onthe first current, perform shaping filtering on the first current andconverting the processed first current to a first voltage for output,and provide the first voltage to the operational amplifier. The secondcircuit is connected to the current source, the operational amplifier,and the third circuit, and is configured to receive a second currentprovided by the current source, provide a fourth voltage to the thirdcircuit based on the second current, perform shaping filtering on thesecond current and converting the processed second current to a secondvoltage for output, and provide the second voltage to the operationalamplifier, where the first current and the second current provided bythe current source are two currents in a differential current. The thirdcircuit is configured to cooperate with the first circuit in performingshaping filtering on the first current and cooperate with the secondcircuit in performing shaping filtering on the second current accordingto the third voltage and the fourth voltage, and the operationalamplifier is configured to provide a small-signal virtual ground pointto the first circuit for the first current to enter the first circuit,and provide a small-signal virtual ground point to the second circuitfor the second current to enter the second circuit.

The TIA in embodiments of this application includes only one operationalamplifier, and has a smaller quantity of operational amplifiers comparedwith a TIA of a second-order active structure shown in FIG. 1B.Therefore, power consumption of the TIA in the embodiments of thisapplication is lower. In addition, the TIA in the embodiments of thisapplication includes the third circuit, and the third circuit cancooperate with the first circuit in performing shaping filtering on thecurrent in the first circuit and cooperate with the second circuit inperforming shaping filtering on the current in the second circuitaccording to the third voltage and the fourth voltage. Therefore,compared with a TIA of a first-order active structure shown in FIG. 1A,filtering performance of the TIA in the embodiments of this applicationis improved, and an out-of-band interference suppression capabilitythereof is further improved.

Based on the first aspect, in a possible design, the first circuitincludes a first part and a second part, the first part and the secondpart are connected in parallel, one end of the parallel connection isconnected to the current source and a negative input of the operationalamplifier, and the other end of the parallel connection is connected toa first output of the operational amplifier, and the first part includesat least one capacitor, and the at least one capacitor is connected inseries and/or in parallel, and the second part includes at least onefirst resistor and at least one second resistor, where the at least onefirst resistor is connected in series and/or in parallel, the at leastone second resistor is connected in series and/or in parallel, the atleast one first resistor is connected in series to the at least onesecond resistor, and a connection point of the series connection isconnected to the third circuit.

According to the foregoing manner, an implementation of the firstcircuit is simplified.

Based on the first aspect, in a possible design, the second circuitincludes a third part and a fourth part, the third part and the fourthpart are connected in parallel, one end of the parallel connection isconnected to the current source and a positive input of the operationalamplifier, and the other end of the parallel connection is connected toa second output of the operational amplifier, and the third partincludes at least one capacitor, and the at least one capacitor isconnected in series and/or in parallel, and the fourth part includes atleast one third resistor and at least one fourth resistor, where the atleast one third resistor is connected in series and/or in parallel, theat least one fourth resistor is connected in series and/or in parallel,the at least one third resistor is connected in series to the at leastone fourth resistor, and a connection point of the series connection isconnected to the third circuit.

According to the foregoing manner, an implementation of the secondcircuit is simplified.

Based on the first aspect, in a possible design, the third circuitincludes at least one capacitor, and the at least one capacitor isconnected in series and/or in parallel.

According to the foregoing manner, an implementation of the thirdcircuit is simplified. Moreover, the third circuit in the foregoingdesign can cooperate with the first circuit and the second circuit inorder to improve a filtering capability, and further improve theout-of-band interference suppression capability of the TIA.

Based on the first aspect, in a possible design, the first circuitincludes a first capacitor, a first resistor, and a second resistor, thefirst resistor and the second resistor are connected in series and thenconnected to the first capacitor in parallel, one end of the parallelconnection is connected to the current source and a negative input ofthe operational amplifier, and the other end of the parallel connectionis connected to a first output of the operational amplifier, and aconnection point of the series connection between the first resistor andthe second resistor is connected to the third circuit.

Based on the first aspect, in a possible design, the second circuitincludes a second capacitor, a third resistor, and a fourth resistor,the third resistor and the fourth resistor are connected in series andthen connected to the second capacitor in parallel, one end of theparallel connection is connected to the current source and a positiveinput of the operational amplifier, and the other end of the parallelconnection is connected to a second output of the operational amplifier,and a connection point of the series connection between the thirdresistor and the fourth resistor is connected to the third circuit, andthe first capacitor and the second capacitor have a same capacitance,and resistances of the first resistor, the second resistor, the thirdresistor, and the fourth resistor are the same.

Based on the first aspect, in a possible design, the third circuitincludes a third capacitor, and the third circuit has a same capacitanceas the first capacitor and the second capacitor.

According to a second aspect, a chip is provided, including the TIA inany possible design provided in the first aspect.

According to a third aspect, a communications device is provided,including the chip provided in the second aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a TIA of a first-order active structure;

FIG. 1B shows a TIA of a second-order active structure;

FIG. 2 is a schematic structural diagram of a TIA according to anembodiment of this application;

FIG. 3A and FIG. 3B are schematic structural diagrams of a first circuitaccording to an embodiment of this application;

FIG. 4A and FIG. 4B are schematic structural diagrams of a secondcircuit according to an embodiment of this application;

FIG. 5 is a schematic structural diagram of a third circuit according toan embodiment of this application;

FIG. 6 is a schematic structural diagram of a TIA according to anembodiment of this application; and

FIG. 7 is a comparison diagram of amplitude-frequency characteristiccurves of a TIA in an embodiment of this application and a TIA of afirst-order active structure.

DESCRIPTION OF EMBODIMENTS

The term “and/or” in the embodiments of this application describes onlyan association relationship for describing associated objects andrepresents that three relationships may exist. For example, A and/or Bmay represent the three cases, only A exists, both A and B exist, andonly B exists. In addition, the character “/” in the embodiments of thisapplication generally indicates an “or” relationship between theassociated objects.

The following further describes the embodiments of this application indetail with reference to the accompanying drawings.

A TIA is configured to convert a current signal to a voltage signal, andmay be integrated into a chip and applied in a communications device,for example, applied to a receiving part of a sensor in thecommunications device or applied in a radio frequency transceiver systemof the communications device.

A TIA in the embodiments of this application includes only oneoperational amplifier, and has a smaller quantity of operationalamplifiers compared with a TIA of a second-order active structure shownin FIG. 1B. Therefore, power consumption of the TIA in the embodimentsof this application is lower. In addition, the TIA in the embodiments ofthis application includes a third circuit, and the third circuit cancooperate with a first circuit in performing shaping filtering on acurrent in the first circuit, and cooperate with a second circuit inperforming shaping filtering on a current in the second circuitaccording to the third voltage and the fourth voltage. Therefore,compared with a TIA of a first-order active structure shown in FIG. 1A,filtering performance of the TIA in the embodiments of this applicationis improved, and an out-of-band interference suppression capabilitythereof is further improved.

As shown in FIG. 2, a TIA 200 in an embodiment of this applicationincludes a first circuit 210, a second circuit 220, a third circuit 230,and an operational amplifier 240. Each of the first circuit 210, thesecond circuit 220, and the third circuit 230 includes a passivecomponent.

The first circuit 210 is connected to a current source, the operationalamplifier 240, and the third circuit 230, and is configured to receive afirst current provided by the current source, provide a third voltage tothe third circuit 230 based on the first current, perform shapingfiltering on the first current and converting the processed firstcurrent to a first voltage for output, and provide the first voltage tothe operational amplifier 240.

A first end 211 of the first circuit 210 is connected to one end of thecurrent source and a negative input 241 of the operational amplifier240, a second end 212 of the first circuit 210 is connected to a firstoutput 242 of the operational amplifier 240, and a third end 213 of thefirst circuit 210 is connected to one end 231 of the third circuit 230.The first circuit 210 is configured to receive the first currentprovided by the current source using the first end 211, provide thethird voltage to the end 231 of the third circuit 230 based on the firstcurrent, perform shaping filtering on the first current and convertingthe processed first current to the first voltage, and output the firstvoltage using the second end 212. Because the second end 212 of thefirst circuit 210 is connected to the first output 242 of theoperational amplifier 240, a voltage of the first output 242 is set tothe first voltage.

The second circuit 220 is connected to the current source, theoperational amplifier 240, and the third circuit 230, and is configuredto receive a second current provided by the current source, provide afourth voltage to the third circuit 230 based on the second current,perform shaping filtering on the second current and converting theprocessed second current to a second voltage for output, and provide thesecond voltage to the operational amplifier 240. The first current andthe second current provided by the current source are two currents in adifferential current.

A first end 221 of the second circuit 220 is connected to the other endof the current source and a positive input 243 of the operationalamplifier 240, a second end 222 of the second circuit 220 is connectedto a second output 244 of the operational amplifier 240, and a third end223 of the second circuit 220 is connected to the other end 232 of thethird circuit 230. The second circuit 220 is configured to receive thesecond current provided by the current source using the first end 221 ofthe second circuit 220, provide the fourth voltage to the other end 232of the third circuit 230 based on the second current, perform shapingfiltering on the second current and converting the processed secondcurrent to the second voltage, and output the second voltage using thesecond end 222. Because the second output 244 of the operationalamplifier 240 is connected to the second end 222, a voltage of thesecond output 244 is set to the second voltage by the second circuit220.

The third circuit 230 is configured to cooperate with the first circuit210 in performing shaping filtering on the first current and cooperatewith the second circuit 220 in performing shaping filtering on thesecond current according to the third voltage and the fourth voltage.

The operational amplifier 240 is configured to provide a small-signalvirtual ground point to the first circuit 210 for the first current toenter the first circuit 210, and provide a small-signal virtual groundpoint to the second circuit 220 for the second current to enter thesecond circuit 220.

The operational amplifier 240 is configured to provide the small-signalvirtual ground points to the first circuit 210 and the second circuit220, respectively.

The operational amplifier 240 provides the small-signal virtual groundpoint to the first end 211 of the first circuit 210 using the negativeinput 241 to make a voltage of the first end 211 set to zero such thatthe first current provided by the current source enters the firstcircuit 210. The operational amplifier 240 provides the small-signalvirtual ground point to the first end 221 of the second circuit 220using the positive input 243 to make a voltage of the first end 221 setto zero such that the second current provided by the current sourceenters the second circuit 220.

It should be understood that, the passive component includes a componentsuch as a capacitor, an inductor, and a resistor. Passive components maybe used to form the first circuit 210, the second circuit 220, and thethird circuit 230 to implement functions in this embodiment of thisapplication. A quantity and type of the passive components are notlimited herein.

In a possible design, the first circuit 210 includes a first part and asecond part, the first part and the second part are connected inparallel, one end (that is, the first end 211) of the parallelconnection is connected to the current source and the negative input 241of the operational amplifier 240, and the other end (that is, the secondend 212) of the parallel connection is connected to the first output 242of the operational amplifier 240.

The first part includes at least one capacitor, and the at least onecapacitor is connected in series and/or in parallel. The second partincludes at least one first resistor and at least one second resistor,where the at least one first resistor is connected in series and/or inparallel, the at least one second resistor is connected in series and/orin parallel, the at least one first resistor is connected in series tothe at least one second resistor, the at least one first resistor isconnected in series to the at least one second resistor, and aconnection point of the series connection is connected to the thirdcircuit 230. Further, the connection point of the series connection isconnected to the end 231 of the third circuit 230, and the connectionpoint of the series connection is the third end 213 of the first circuit210.

For example, in a first circuit 210 shown in FIG. 3A, a first partincludes three capacitors C1, C2, and C3, and a second part includes afirst resistor R1 and a second resistor R2. In a first circuit 210 shownin FIG. 3B, a first part includes a capacitor C1, and a second partincludes a first resistor R1, a first resistor R2, and a second resistorR3. In addition to connection manners of the first circuit 210 shown inFIG. 3A and FIG. 3B, for the first circuit 210 in this embodiment ofthis application, there may be another connection manner equivalent tothose in FIG. 3A and FIG. 3B.

In a possible implementation, for example, the second circuit 220includes a third part and a fourth part in parallel, one end (that is,the first end 221) of the parallel connection is connected to thecurrent source and the positive input 243 of the operational amplifier240, and the other end (that is, the second end 222) of the parallelconnection is connected to the second output 244 of the operationalamplifier 240.

The third part includes at least one capacitor, and the at least onecapacitor is connected in series and/or in parallel. The fourth partincludes at least one third resistor and at least one fourth resistor,where the at least one third resistor is connected in series and/or inparallel, the at least one fourth resistor is connected in series and/orin parallel, the at least one third resistor is connected in series tothe at least one fourth resistor, and a connection point of the seriesconnection is connected to the third circuit 230. Further, theconnection point of the series connection is connected to the other end232 of the third circuit 230, and the connection point of the seriesconnection is the third end 223 of the second circuit 220.

For example, in a second circuit 220 shown in FIG. 4A, a third partincludes four capacitors C1, C2, C3, and C4, and a fourth part includesa third resistor R1 and a fourth resistor R2. In a second circuit 220shown in FIG. 4B, a third part includes a capacitor C1, and a fourthpart includes a third resistor R1, a third resistor R2, and a fourthresistor R3. In addition to connection manners of the second circuit 220shown in FIG. 4A and FIG. 4B, for the second circuit 220 in thisembodiment of this application, there may be another connection mannerequivalent to those in FIG. 4A and FIG. 4B.

It should be understood that, the connection manners of the firstcircuit 210 and the second circuit 220 may be the same or may bedifferent, and a quantity of capacitors and quantities of firstresistors, second resistors, third resistors, and fourth resistors inthe first circuit 210 and the second circuit 220 are not limited.

In a possible design, the third circuit 230 includes at least onecapacitor, and the at least one capacitor is connected in series and/orin parallel.

For example, if the third circuit 230 includes two capacitors C1 and C2,as shown in FIG. 5, C1 and C2 are connected in parallel in the thirdcircuit 230. One end of the third circuit 230 is connected to the thirdend 213 of the first circuit 210, and the other end of the third circuit230 is connected to the third end 223 of the second circuit 220. Itshould be understood that, a quantity of capacitors included in thethird circuit 230 is not limited in this embodiment of this application.

It should be noted that, in this embodiment of this application, aresistance and a capacitance may be set according to an actual need, toobtain a required voltage.

The following uses a TIA shown in FIG. 6 as an example and assumes thata gain of an operational amplifier within an operating frequency rangeis infinite to perform qualitative analysis on the TIA in theembodiments of this application using a small-signal equation.

As shown in FIG. 6, the TIA includes capacitors C1, C2, and C3,resistors R1, R2, R3, and R4, and an operational amplifier. A currentsource provides a differential current to the TIA, C1, R1, and R2 form afirst circuit, C3 forms a third circuit, and C2, R3, and R4 form asecond circuit. A current of the differential current flows into thefirst circuit through p1, and the other current of the differentialcurrent flows into the second circuit through n1.

A negative input of the operational amplifier provides a small-signalvirtual ground point to the first circuit, and a positive input of theoperational amplifier provides a small-signal virtual ground point tothe second circuit. It is assumed that voltages at a point a, a point b,a point p2, and a point n2 shown in FIG. 6 are Va, Vb, Vp, and Vn,respectively, a current that the current source provides to the firstcircuit is i1, and a current that the current source provides to thesecond circuit is i2, a sum of currents that flow through the point a,the point b, a point c, and a point d respectively is zero. In thiscase, the following formulas are obtained:

$\begin{matrix}{{\frac{\left( {{Va} - 0} \right)}{R\; 1} + \frac{\left( {{Va} - {Vp}} \right)}{R\; 2} + \frac{\left( {{Va} - {Vb}} \right)}{\frac{1}{j\;\omega\; C\; 3}}} = 0} & (1) \\{{\frac{\left( {{Vb} - 0} \right)}{R\; 3} + \frac{\left( {{Vb} - {Vn}} \right)}{R\; 4} + \frac{\left( {{Vb} - {Va}} \right)}{\frac{1}{j\;\omega\; C\; 3}}} = 0} & (2) \\{{{{- i}\; 1} + \frac{\left( {0 - {Va}} \right)}{R\; 1} + \frac{\left( {0 - {Vp}} \right)}{\frac{1}{j\;\omega\; C\; 1}}} = 0} & (3) \\{{{{- i}\; 2} + \frac{\left( {0 - {Vb}} \right)}{R\; 3} + \frac{\left( {0 - {Vn}} \right)}{\frac{1}{j\;\omega\; C\; 2}}} = 0} & (4)\end{matrix}$where ω indicates an operating frequency, when R1=R2=R3=R4=R andC1=C2=C3=C, a transfer function is obtained as follows:

$\frac{Vout}{Iin} = {\frac{{Vp} - {Vn}}{{i\; 1} - {i\; 2}} = {\frac{2{R\left( {1 + {{R \cdot C \cdot j}\;\omega}} \right)}}{1 + {2{R \cdot C \cdot j}\;\omega} + {2{R^{2} \cdot C^{2} \cdot \left( {j\;\omega} \right)^{2}}}}.}}$

It can be learned from the transfer function that, the transfer functionincludes two poles and one zero, and the zero and one pole form azero-pole pair on a near passband. Compared with a first-order active RCstructure, in-band flatness of the TIA in the embodiments of thisapplication is improved. If a same 3 decibels (dB) corner frequency isused, the TIA in the embodiments of this application has a betterout-of-band suppression characteristic compared with a TIA of afirst-order active structure. As shown in FIG. 7, a curve 1 is anamplitude-frequency characteristic curve when R1=R2=R3=R4=R andC1=C2=C3=C, while a curve 2 is an amplitude-frequency characteristiccurve of a TIA that is of a first-order active structure and to which C3is not added. It can be learned from FIG. 7 that, the TIA in theembodiments of this application has a second-order characteristic on anear passband and has better flatness. In FIG. 7, 3 dB cornerfrequencies of the curve 1 and the curve 2 are different. The 3 dBcorner frequency of the curve 1 is A, and the 3 dB corner frequency ofthe curve 2 is B. If the TIA in the embodiments of this application hasa same 3 dB corner frequency requirement as the TIA of the first-orderactive structure, the amplitude-frequency characteristic curve in theembodiments of this application has a better out-of-band suppressioncharacteristic. In addition, the TIA in the embodiments of thisapplication uses only one operational amplifier such that powerconsumption of the TIA is reduced compared with a TIA of a second-orderactive structure.

In addition, the embodiments of this application further provide a chip,including any TIA provided in the embodiments of this application.

The embodiments of this application further provide a communicationsdevice, including the chip provided in the embodiments of thisapplication.

For a connection manner of a TIA in the chip or in the communicationsdevice, refer to the connection manner of the TIA shown in FIG. 2.Details are not described herein.

Although some specific embodiments that can be implemented have beendescribed, persons skilled in the art can make changes and modificationsto these embodiments once they learn the basic inventive concept.Therefore, the following claims are intended to be construed to coverthe embodiments described in this application and all changes andmodifications falling within the scope of this application.

Obviously, persons skilled in the art can make various modifications andvariations to this application without departing from the spirit andscope of this application. This application is intended to cover thesemodifications and variations of this application provided that they fallwithin the scope of protection defined by the following claims and theirequivalent technologies.

The invention claimed is:
 1. An amplifier circuit, comprising: a thirdcircuit comprising a first end and a third circuit passive component; asingle operational amplifier; a first circuit coupled to the thirdcircuit and the operational amplifier and including a plurality ofresistors, wherein the first circuit is configured to: receive a firstsignal from a signal source; provide a third voltage to the thirdcircuit based on the first signal; perform shape filtering on the firstsignal; convert a shape filtered first signal to a first voltage foroutput; and provide the first voltage to the operational amplifier; anda second circuit coupled to the signal source, the operationalamplifier, and the third circuit, wherein the second circuit comprises asecond circuit passive component, and wherein the second circuit isconfigured to: receive a second signal from the signal source; provide afourth voltage to the third circuit based on the second signal; performthe shape filtering on the second signal; convert a shape filteredsecond signal to a second voltage for output; and provide the secondvoltage to the operational amplifier, wherein the first signal and thesecond signal received from the signal source are two signals in adifferential signal; wherein the first end of the third circuit iscoupled between at least two of the plurality of resistors in the firstcircuit; wherein the third circuit is configured to: cooperate with thefirst circuit to perform shape filtering on the first signal accordingto the third voltage; and cooperate with the second circuit to performshape filtering on the second signal according to the fourth voltage,and wherein the operational amplifier is configured to: provide asmall-signal virtual ground point to the first circuit for the firstsignal to enter the first circuit; and provide a small-signal virtualground point to the second circuit for the second signal to enter thesecond circuit.
 2. The amplifier circuit of claim 1, wherein the firstcircuit comprises a first part and a second part, wherein the first partand the second part are coupled in parallel, wherein one end of theparallel coupling is coupled to the signal source and a negative inputof the operational amplifier, wherein the other end of the parallelcoupling is coupled to a first output of the operational amplifier,wherein the first part comprises at least one capacitor, wherein the atleast one capacitor is coupled in series or in parallel, wherein thesecond part comprises the plurality of resistors, wherein at least onefirst resistor of the plurality of resistors is coupled in series or inparallel, wherein at least one second resistor of the plurality ofresistors is coupled in series or in parallel, wherein the at least onefirst resistor is coupled in series to the at least one second resistor,and wherein a coupling point of the series coupling between the at leastone first resistor and the at least one second resistor is coupled tothe third circuit.
 3. The amplifier circuit of claim 1, wherein thesecond circuit comprises a third part and a fourth part, wherein thethird part and the fourth part are coupled in parallel, wherein one endof the parallel coupling is coupled to the signal source and a positiveinput of the operational amplifier, wherein the other end of theparallel coupling is coupled to a second output of the operationalamplifier, wherein the third part comprises at least one capacitor,wherein the at least one capacitor is coupled in series or in parallel,wherein the fourth part comprises at least one third resistor and atleast one fourth resistor, wherein the at least one third resistor iscoupled in series or in parallel, wherein the at least one fourthresistor is coupled in series or in parallel, wherein the at least onethird resistor is coupled in series to the at least one fourth resistor,and wherein a coupling point of the series coupling between the at leastone third resistor and the at least one fourth resistor is coupled tothe third circuit.
 4. The amplifier circuit of claim 1, wherein thethird circuit comprises a plurality of capacitors, and wherein theplurality of capacitors are coupled in parallel.
 5. The amplifiercircuit of claim 1, wherein the first circuit comprises a firstcapacitor, wherein the plurality of resistors includes a first resistorand a second resistor, wherein the first resistor and the secondresistor are coupled in series and coupled to the first capacitor inparallel, wherein one end of the parallel coupling is coupled to thesignal source and a negative input of the operational amplifier, whereinthe other end of the parallel coupling is coupled to a first output ofthe operational amplifier, and wherein a coupling point of the seriescoupling between the first resistor and the second resistor is coupledto the third circuit.
 6. The amplifier circuit of claim 5, wherein thesecond circuit comprises a second capacitor, a third resistor, and afourth resistor, wherein the third resistor and the fourth resistor arecoupled in series and coupled to the second capacitor in parallel,wherein one end of the parallel coupling is coupled to the signal sourceand a positive input of the operational amplifier, wherein the other endof the parallel coupling is coupled to a second output of theoperational amplifier, wherein a coupling point of the series couplingbetween the third resistor and the fourth resistor is coupled to thethird circuit, wherein the first capacitor and the second capacitor havea same capacitance, and wherein resistances of the first resistor, thesecond resistor, the third resistor, and the fourth resistor are thesame.
 7. The amplifier circuit of claim 6, wherein the third circuitcomprises a third capacitor, and wherein the third circuit has a samecapacitance as the first capacitor and the second capacitor.
 8. Anamplifier circuit, comprising: a third circuit comprising a first endand a third circuit passive component; a single operational amplifier; afirst circuit coupled to the operational amplifier and the third circuitand including a plurality of resistors, wherein the first circuit isconfigured to: receive a first signal from a signal source; provide athird voltage to a third circuit based on the first signal; performshape filtering on the first signal; convert a shape filtered firstsignal to a first voltage for output; and provide the first voltage tothe operational amplifier; and a second circuit coupled to the signalsource, the operational amplifier, and the third circuit, wherein thesecond circuit includes a plurality of capacitors, and wherein thesecond circuit is configured to: receive a second signal from the signalsource; provide a fourth voltage to the third circuit based on thesecond signal; perform the shape filtering on the second signal; converta shape filtered second signal to a second voltage for output; andprovide the second voltage to the operational amplifier, wherein thefirst end of the third circuit is coupled between at least two of theplurality of resistors in the first circuit, wherein the first signaland the second signal received from the signal source are two signals ina differential signal, wherein the third circuit is configured to:cooperate with the first circuit to perform the shape filtering on thefirst signal according to the third voltage; and cooperate with thesecond circuit to perform the shape filtering on the second signalaccording to the fourth voltage, and wherein the operational amplifieris configured to: provide a small-signal virtual ground point to thefirst circuit for the first signal to enter the first circuit; andprovide a small-signal virtual ground point to the second circuit forthe second signal to enter the second circuit.
 9. The amplifier circuitof claim 8, wherein the first circuit comprises a first part and asecond part, wherein the first part and the second part are coupled inparallel, wherein one end of the parallel coupling is coupled to thesignal source and a negative input of the operational amplifier, whereinthe other end of the parallel coupling is coupled to a first output ofthe operational amplifier, wherein the first part comprises at least onecapacitor, wherein the at least one capacitor is coupled in series or inparallel, wherein the second part comprises the plurality of resistors,wherein the plurality of resistors includes at least one first resistorand at least one second resistor, wherein the at least one firstresistor is coupled in series or in parallel, wherein the at least onesecond resistor is coupled in series or in parallel, wherein the atleast one first resistor is coupled in series to the at least one secondresistor, and wherein a coupling point of the series coupling betweenthe at least one first resistor and the at least one second resistor iscoupled to the third circuit.
 10. The amplifier circuit of claim 8,wherein the second circuit comprises a third part and a fourth part,wherein the third part and the fourth part are coupled in parallel,wherein one end of the parallel coupling is coupled to the signal sourceand a positive input of the operational amplifier, wherein the other endof the parallel coupling is coupled to a second output of theoperational amplifier, wherein the third part comprises the plurality ofcapacitors, wherein the plurality of capacitors are coupled in series orin parallel, wherein the fourth part comprises at least one thirdresistor and at least one fourth resistor, wherein the at least onethird resistor is coupled in series or in parallel, wherein the at leastone fourth resistor is coupled in series or in parallel, wherein the atleast one third resistor is coupled in series to the at least one fourthresistor, and wherein a coupling point of the series coupling betweenthe at least one third resistor and the at least one fourth resistor iscoupled to the third circuit.
 11. The amplifier circuit of claim 8,wherein the third circuit comprises at least one capacitor, and whereinthe at least one capacitor is coupled in parallel.
 12. The amplifiercircuit of claim 8, wherein the first circuit comprises a firstcapacitor, wherein the plurality of resistors comprises a first resistorand a second resistor, wherein the first resistor and the secondresistor are coupled in series and coupled to the first capacitor inparallel, wherein one end of the parallel coupling is coupled to thesignal source and a negative input of the operational amplifier, whereinthe other end of the parallel coupling is coupled to a first output ofthe operational amplifier, and wherein a coupling point of the seriescoupling between the first resistor and the second resistor is coupledto the third circuit.
 13. The amplifier circuit of claim 12, wherein theplurality of capacitors of the second circuit comprises a secondcapacitor, wherein the second circuit comprises a third resistor and afourth resistor, wherein the third resistor and the fourth resistor arecoupled in series and coupled to the second capacitor in parallel,wherein one end of the parallel coupling is coupled to the signal sourceand a positive input of the operational amplifier, wherein the other endof the parallel coupling is coupled to a second output of theoperational amplifier, wherein a coupling point of the series couplingbetween the third resistor and the fourth resistor is coupled to thethird circuit, wherein the first capacitor and the second capacitor havea same capacitance, and wherein resistances of the first resistor, thesecond resistor, the third resistor, and the fourth resistor are thesame.
 14. The amplifier circuit of claim 13, wherein the third circuitcomprises a third capacitor, and wherein the third circuit has a samecapacitance as the first capacitor and the second capacitor.
 15. Acommunications device, comprising: a chip; and an amplifier circuitintegrated into the chip, wherein the amplifier circuit comprises: athird circuit including a first end and a third circuit passivecomponent; a single operational amplifier; a first circuit coupled tothe third circuit and the operational amplifier and including aplurality of resistors, wherein the first circuit is configured to:receive a first signal from a signal source; provide a third voltage toa third circuit based on the first signal; perform shape filtering onthe first signal; convert a shape filtered first signal to a firstvoltage for output; and provide the first voltage to the operationalamplifier; and a second circuit coupled to the signal source, theoperational amplifier, and the third circuit, wherein the second circuitincludes a second circuit passive component, and wherein the secondcircuit is configured to: receive a second signal from the signalsource; provide a fourth voltage to the third circuit based on thesecond signal; perform the shape filtering on the second signal; converta shape filtered second signal to a second voltage for output; andprovide the second voltage to the operational amplifier, wherein thefirst signal and the second signal received from the signal source aretwo signals in a differential signal, wherein the first end of the thirdcircuit is coupled between at least two of the plurality of resistors inthe first circuit; wherein the third circuit is configured to: cooperatewith the first circuit to perform the shape filtering on the firstsignal; and cooperate with the second circuit to perform the shapefiltering on the second signal according to the third voltage and thefourth voltage, and wherein the operational amplifier is configured to:provide a small-signal virtual ground point to the first circuit for thefirst signal to enter the first circuit; and provide a small-signalvirtual ground point to the second circuit for the second signal toenter the second circuit.
 16. The communications device of claim 15,wherein the first circuit comprises a first part and a second part,wherein the first part and the second part are coupled in parallel,wherein one end of the parallel coupling is coupled to the signal sourceand a negative input of the operational amplifier, wherein the other endof the parallel coupling is coupled to a first output of the operationalamplifier, wherein the first part comprises at least one capacitor,wherein the at least one capacitor is coupled in series or in parallel,wherein the second part comprises the plurality of resistors, whereinthe plurality of resistors includes at least one first resistor and atleast one second resistor, wherein the at least one first resistor iscoupled in series or in parallel, wherein the at least one secondresistor is coupled in series or in parallel, wherein the at least onefirst resistor is coupled in series to the at least one second resistor,and wherein a coupling point of the series coupling between the at leastone first resistor and the at least one second resistor is coupled tothe third circuit.
 17. The communications device of claim 15, whereinthe second circuit comprises a third part and a fourth part, wherein thethird part and the fourth part are coupled in parallel, wherein one endof the parallel coupling is coupled to the signal source and a positiveinput of the operational amplifier, wherein the other end of theparallel coupling is coupled to a second output of the operationalamplifier, wherein the third part comprises at least one capacitor,wherein the at least one capacitor is coupled in series or in parallel,wherein the fourth part comprises at least one third resistor and atleast one fourth resistor, wherein the at least one third resistor iscoupled in series or in parallel, wherein the at least one fourthresistor is coupled in series or in parallel, wherein the at least onethird resistor is coupled in series to the at least one fourth resistor,and wherein a coupling point of the series coupling between the at leastone third resistor and the at least one fourth resistor is coupled tothe third circuit.
 18. The communications device of claim 15, whereinthe third circuit comprises at least one capacitor, and wherein the atleast one capacitor is coupled in series or in parallel.
 19. Thecommunications device of claim 15, wherein the first circuit comprises afirst capacitor, wherein the plurality of resistors comprises a firstresistor and a second resistor, wherein the first resistor and thesecond resistor are coupled in series and coupled to the first capacitorin parallel, wherein one end of the parallel coupling is coupled to thesignal source and a negative input of the operational amplifier, whereinthe other end of the parallel coupling is coupled to a first output ofthe operational amplifier, and wherein a coupling point of the seriescoupling between the first resistor and the second resistor is coupledto the third circuit.
 20. The communications device of claim 19, whereinthe second circuit comprises a second capacitor, a third resistor and afourth resistor, wherein the third resistor and the fourth resistor arecoupled in series and coupled to the second capacitor in parallel,wherein one end of the parallel coupling is coupled to the signal sourceand a positive input of the operational amplifier, wherein the other endof the parallel coupling is coupled to a second output of theoperational amplifier, wherein a coupling point of the series couplingbetween the third resistor and the fourth resistor is coupled to thethird circuit, wherein the first capacitor and the second capacitor havea same capacitance, and wherein resistances of the first resistor, thesecond resistor, the third resistor, and the fourth resistor are thesame.
 21. An amplifier circuit, comprising: an amplifier comprising apair of inputs configured for receiving a differential signal, a firstoutput, and a second output; a first resistor and a second resistor,wherein the first resistor and the second resistor are disposed inseries and coupled to a first input of the pair of inputs; a thirdresistor and a fourth resistor, wherein the third resistor and thefourth resistor are disposed in series and coupled to a second input ofthe pair of inputs; and a first capacitor, a second capacitor, and athird capacitor, wherein the first capacitor comprises a first end and asecond end, wherein the first end of the first capacitor is coupled to afirst point between the first resistor and the second resistor, andwherein the second end of the capacitor is coupled to a second pointbetween the third resistor and the fourth resistor, wherein the secondcapacitor is disposed between the first input and the first output, andwherein the third capacitor is disposed between the second input and thesecond output.
 22. The amplifier circuit of claim 21, further comprisinga first capacitor circuit and a second capacitor circuit, wherein thefirst capacitor circuit is disposed between the first input and thefirst output, and wherein the second capacitor circuit is disposedbetween the second input and the second output.
 23. The amplifiercircuit of claim 22, wherein the first capacitor circuit comprises atleast two capacitors disposed in parallel or in series, wherein thesecond circuit comprises at least two capacitors disposed in parallel orin series.
 24. The amplifier circuit of claim 21, wherein the amplifieris an operational amplifier.